====== Integrate EMG ======

===== Linear Envelope =====

=== Computing the EMG Envelope using rectify and lowpass filter ===

This section will compute the EMG Envelope using rectify and lowpass filter. Rectify takes the absolute value of every element of a signal. Visual3D calculates signal rectification using the following formula: x(ti)= abs(x(ti))

=== Lowpass Filter Cutoff ===

The default lowpass filter in Visual3D is a fourth order butterworth filter.

Butterworth filters have an upper limit on the magnitude of the cutoff frequency.

The maximum theoretical cutoff frequency is (sampling_rate*0.802/2).

VIsual3D is a little more conservative than that because we have found the filter to be unreliable at the theoretical limits.

The highest cutoff frequency that VIsual3D will allow you is 0.393* sampling-rate.

If your EMG signals are sampled at 1000 Hz, the highest cutoff frequency is 393 Hz.

=== Example Script ===

The highpass filter is not part of the linear envelope, but is used to remove the [[Visual3D:Documentation:EMG:Processing:Detecting_Muscle_Onset|DC offset]].

<code>
! Apply high pass filter with 50 hz cutoff
Highpass_Filter 
/Signal_Types=ANALOG 
/SIgnal_Names=EMG1+EMG2+EMG3 
/Signal_Folder=ORIGINAL 
! /Result_Suffix= 
/Result_Folder=HIGHPASS
! /Filter_Class=BUTTERWORTH 
/Frequency_Cutoff=50 
/Num_Reflected= 0 
/Total_Buffer_Size=100 
/Num_Bidirectional_Passes=1 
; 

! Rectify the signals
Rectify
/SIGNAL_TYPES=ANALOG
/SIGNAL_NAMES=EMG1+EMG2+EMG3
/SIGNAL_FOLDER=HIGHPASS 
! /RESULT_NAMES=
! /RESULT_TYPES=
/RESULT_FOLDER=RECTIFY 
! /RESULT_SUFFIX=
;

! Apply a low pass filter
Lowpass_Filter  
/Signal_Types= ANALOG 
/Signal_Names= EMG1+EMG2+EMG3 
/Signal_Folder= RECTIFY 
! /Result_Suffix= 
/Result_Folder=LOWPASS
/Frequency_Cutoff=10 
/Num_Reflected=50
;
</code>